Fix parser::parse_names() not to fail on pattern inclusion groups for some corner cases

Specifically, fix the function for the case when the pattern inclusion group
is specified first in the pattern group in a directory. For example, before
the fix, compiling the following buildfile:

fs = hello
exe{hello}: foo/{hxx ixx txx cxx}{+{$fs}}

would fail with the following error:

invalid 'foo/hello' in name pattern

0 files changed, 0 insertions, 0 deletions